Proteomic Identification of Plasma Biomarkers of Response to IL‐5 Inhibitor Biologics in Healthy Subjects

Proteomics can identify pharmacodynamic (PD) biomarkers by detecting protein changes in response to drug treatment, providing insights into drug mechanism and biological effects. In this study, we profiled over 7000 plasma proteins to identify potential PD biomarkers for the interleukin-5 (IL-5) inhibitors mepolizumab and reslizumab, which are approved for treating eosinophilic asthma. We used longitudinal plasma samples from healthy participants treated with a single dose of mepolizumab (n = 8, 24 mg) or reslizumab (n = 8, 0.8 mg/kg), or placebo (n = 8) to identify differentially expressed proteins. We then characterized PD biomarker candidates by their magnitude of response, area under the effect curve (AUEC), dose-response, variability, and replication of response at a lower dose for mepolizumab (n = 8, 12 mg) or reslizumab (n = 8, 0.4 mg/kg) compared to placebo. Eosinophil major basic protein (EMBP) and proteoglycan-3 (PRG3) were differentially expressed in response to mepolizumab and reslizumab, respectively, achieving Bonferroni-adjusted statistical significance (p-value < 6.86E-06) and nominal significance (p-value < 5.0E-05) with the other IL-5 inhibitor. EMBP showed a > 20% fold change difference with mepolizumab (24 mg) versus placebo at peak time, and PRG3 demonstrated a > 20% fold change with reslizumab (0.8 mg/kg) versus placebo at peak time. Both proteins had significant AUEC with both drug doses, with EMBP AUEC only significant (absolute AUEC high > low dose) at the higher mepolizumab dose. Both biomarkers showed dose-response trends and comparable variability to placebo. Our study identified EMBP and PRG3 as promising plasma PD biomarkers for IL-5 inhibitors, warranting further validation for early phase trials and biosimilar development programs.